What stimulates smooth muscles to contract?
Smooth muscles are stimulated to contract by catecholamines released by nerves in the vicinity of the muscle, as well as by a number of other hormones. Smooth muscles are also stimulated by the catecholamines in the bloodstream that originate in the secretions of the adrenal medulla. These hormones diffuse over the entire smooth muscle cell.
How do hormones affect smooth muscle contraction?
Effects of Hormones on Smooth Muscle Contraction. Mostcirculating hormones in the blood affect smooth muscle contraction to some degree, and some have profound effects. Among the more important of these are norepinephrine, epinephrine, acetylcholine,angiotensin, endothelin, vasopressin, oxytocin, sero-tonin, and histamine.
How does the nervous system stimulate muscle contraction?
Although skeletal muscle fibers are stimulated exclu-sively by the nervous system, smooth muscle can be stimulated to contract by multiple types of signals: by nervous signals, by hormonal stimulation, by stretch of the muscle, and in several other ways. Nervous and Hormonal Control of Smooth Muscle Contraction.
What is the role of myosin in muscle contraction?
Energy released from ATP by myosin ATPase activity results in the cycling of the myosin cross-bridges with actin for contraction. Thus contractile activity in smooth muscle is determined primarily by the phosphorylation state of the light chain of myosin—a highly regulated process.
What is the control of smooth muscle contraction?
Nervous and Hormonal Control of Smooth Muscle Contraction. Although skeletal muscle fibers are stimulated exclu-sively by the nervous system, smooth muscle can be stimulated to contract by multiple types of signals: by nervous signals, by hormonal stimulation, by stretch of the muscle, and in several other ways.
What are the neuromuscular junctions of smooth muscle?
Physiologic Anatomy of Smooth Muscle Neuromuscular Junc-tions. Neuromuscular junctions of the highly struc-tured type found on skeletal muscle fibers do not occur in smooth muscle. Instead, the autonomic nerve fibers that innervate smooth muscle generally branch.
What is the function of contact junctions?
These are called contact junctions, and they function in much the sameway as the skeletal muscle neuromuscular junction; the rapidity of contraction of these smooth muscle fibers is considerably faster than that of fibers stimulated by the diffuse junctions. Excitatory and Inhibitory Transmitter Substances Secreted at the Smooth Muscle ...
How many nanometers are in a smooth muscle cell?
In a few instances, particularly in the multi-unit type of smooth muscle, the varicosities are separated from the muscle cell membrane by as little as 20 to 30 nanometers —the same width as the synaptic cleft that occurs in the skeletal muscle junction. These are called contact junctions, and they function in much the sameway as ...
How does muscle excitation travel?
Furthermore, where there are many layers of muscle cells, the nerve fibers often innervate only the outer layer, and muscle excitation travels from this outer layer to the inner layers by action potential con-duction in the muscle mass or by additional diffusion of the transmitter substance.
When visceral (unitary) smooth muscle is stretched sufficiently, spontaneous action potentials usually are generated?
When visceral (unitary) smooth muscle is stretched sufficiently, spontaneous action potentials usually are generated. They result from a combination of (1) the normal slow wave potentials and (2) decrease in overall negativity of the membrane potential caused by the stretch itself.
Which nerve fibers contain acetylcholine?
But, in contrast to the vesicles of skeletal muscle junctions, which always contain acetylcholine, the vesicles of the autonomic nerve fiber endings contain acetylcholine in some fibers and norepinephrine in others—and occasionally other substances as well. In a few instances, particularly in the multi-unit type of smooth muscle, ...
Types of Smooth Muscle
There are 2 primary types of smooth muscle tissue: single- and multi-unit types.
Stimulation of Smooth Muscle Cells
In skeletal muscle, the stimulus for a muscle fiber to contract always comes via a motor neuron. Smooth muscle, however, may be stimulated in a variety of ways.
Excitation–Contraction Coupling in Smooth Muscle
Like skeletal muscle, smooth muscle requires an influx of Ca 2+ into the sarcoplasm Sarcoplasm Types of Muscle Tissue in order to initiate a contraction. Smooth muscle, however, uses different processes to achieve this influx of Ca 2+: Ca-induced Ca release Release Release of a virus from the host cell following virus assembly and maturation.
Contraction and Relaxation of Smooth Muscle Tissue
Unlike in skeletal muscle, actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin.
How do smooth muscles contract?
Smooth muscles are stimulated to contract by catecholamines released by nerves in the vicinity of the muscle, as well as by a number of other hormones.
What is the force in a smooth muscle?
Force in Smooth Muscle Arises from Ca 2+ Activation of Actin–Myosin Interaction. Smooth muscles contain thick and thin filaments, composed predominantly of myosin and actin, respectively. However, their arrangement is quite different from the striated muscles. The filaments are not organized into sarcomeres, and the ratio ...
What is SMA in hepatitis?
SMA, usually with a V pattern and at low titer, are also a common finding during viral diseases such as infectious mononucleosis and chronic hepatitis C (8–10%), as well as in several rheumatologic and neoplastic diseases. View chapter Purchase book. Read full chapter.
How does ACh affect the membrane potential of small intestinal smooth muscle?
Effects of ACh on the membrane potential of small intestinal smooth muscle in vitro. The sharp spike potential occurs when the circular muscle contracts, and it is superimposed upon the slow wave activity. ACh can modulate the signal by raising the base membrane potential and increasing the spike frequency with a large increase in tonic tension.
What organelle is found in smooth muscle?
Genetic analysis of polycystic kidney disease in humans and patterning of the neural axis in mice led to the common finding that primary cilia are specialized vertebrate mechanochemical signaling organelles present in a wide variety of cell types, including smooth muscle.
What is intrinsic diversity in smooth muscle?
Considerable intrinsic diversity is found among smooth muscle subtypes as a result of differences in their embryonic origins and lineage histories. This epigenetic diversity is evident in adult tissues and prepatterns responses obtained to a common stimulus, e.g., activation of TGF-β signaling pathways (1,8,21). These intrinsic differences in SMC subtypes present attractive therapeutic targets as they offer advantages of inherent specificity over current broadly acting systemic agents. Novel approaches to smooth muscle degenerative diseases, particularly for vascular smooth muscle, are suggested by the recent characterization of resident SMC progenitor cells in the adventitia of mouse and human artery wall. These SMC progenitor cells are dependent on Shh signaling for proliferation and survival in the adventitia. Directed expansion of this progenitor pool may provide additional tools to repair large artery walls whose integrity or function is compromised by medial dissection, progressive calcification or aneurysmal dilation. Genetic analysis of polycystic kidney disease in humans and patterning of the neural axis in mice led to the common finding that primary cilia are specialized vertebrate mechanochemical signaling organelles present in a wide variety of cell types, including smooth muscle. The functions of primary cilia in smooth muscle tissues are just beginning to be defined but the possibilities for their roles as biosensors of mechanical forces suggest a potentially rewarding area for future studies. Finally, advances in our understanding of molecular genetic mechanisms for stage-specific SMC specification in embryonic and adult progenitor cells will provide the information necessary to target direct somatic cell reprogramming approaches and cell-based therapies to smooth muscle tissues in the near future.
Where are smooth muscle cells located?
Smooth muscle is spindle-shaped cells with one centrally located nucleus and no externally visible striations. It is found mainly in the walls of hollow organs. Muscles of small intestine like other unitary smooth muscles have many gap junctional connections between individual cells and act as one sheet in a coordinated fashion. The outstanding characteristic of the small intestinal muscle is its rhythmicity which is alternate contractions and relaxations at a regular frequency at regularly spaced intervals called segments along a section of the intestine [13]. A sharp spike superimposed upon the small sinusoidal wave activity occurs when the circular muscle contracts. The peristaltic contraction makes a rise in the tone level without any interruption in the rhythm of segmental contractions. Thus, the muscle fiber does not need to have an individual innervation and depolarization of one fiber triggers synchronous depolarization throughout the bundle, which are independent of its nerve supply and cause continuous rhythmic partial contractions. Nerve impulses or neurotropic drugs such as ACh and EPI can modulate its motility.
How is smooth muscle cell contraction regulated?
In the intact body, the process of smooth muscle cell contraction is regulated principally by receptor and mechanical (stretch) activation of the contractile proteins myosin and actin. A change in membrane potential, brought on by the firing of action potentials or by activation of stretch-dependent ion channels in the plasma membrane, can also trigger contraction. For contraction to occur, myosin light chain kinase (MLC kinase) must phosphorylate the 20-kDa light chain of myosin, enabling the molecular interaction of myosin with actin. Energy released from ATP by myosin ATPase activity results in the cycling of the myosin cross-bridges with actin for contraction. Thus contractile activity in smooth muscle is determined primarily by the phosphorylation state of the light chain of myosin—a highly regulated process. In some smooth muscle cells, the phosphorylation of the light chain of myosin is maintained at a low level in the absence of external stimuli (i.e., no receptor or mechanical activation). This activity results in what is known as smooth muscle tone and its intensity can be varied.
What is the contractile state of smooth muscle?
In addition, the contractile state of smooth muscle is controlled by hormones, autocrine/paracrine agents, and other local chemical signals.
How does smooth muscle relax?
Smooth muscle relaxation occurs either as a result of removal of the contractile stimulus or by the direct action of a substance that stimulates inhibition of the contractile mechanism. Regardless, the process of relaxation requires a decreased intracellular Ca 2+ concentration and increased MLC phosphatase activity. The sarcoplasmic reticulum and the plasma membrane contain Ca,Mg-ATPases that remove Ca 2+ from the cytosol. Na + /Ca 2+ exchangers are also located on the plasma membrane and aid in decreasing intracellular Ca 2+. During relaxation, receptor- and voltage-operated Ca 2+ channels in the plasma membrane close resulting in a reduced Ca 2+ entry into the cell.
What kinase is responsible for the contraction of myosin?
For contraction to occur, myosin light chain kinase (MLC kinase) must phosphorylate the 20-kDa light chain of myosin, enabling the molecular interaction of myosin with actin. Energy released from ATP by myosin ATPase activity results in the cycling of the myosin cross-bridges with actin for contraction.
What is the phosphorylation of myosin?
In some smooth muscle cells, the phosphorylation of the light chain of myosin is maintained at a low level in the absence of external stimuli (i.e., no receptor or mechanical activation). This activity results in what is known as smooth muscle tone and its intensity can be varied.
Why is smooth muscle called smooth muscle?
Smooth muscle derives its name from the fact that it lacks the striations characteristic of cardiac and skeletal muscle. Layers of smooth muscle cells line the walls of various organs and tubes, and the contractile function of smooth muscle is not under voluntary control.
What is the effect of PKC on smooth muscle contraction?
In many cases, PKC has contraction-promoting effects such as phosphorylation of L- type Ca 2+ channels or other proteins that regulate cross-bridge cycling. Phorbol esters, a group of synthetic compounds known to activate PKC, mimic the action of DG and cause contraction of smooth muscle.
Which hormone stimulates growth of pubic hair?
b. Stimulated by secretion of ACTH, stimulates growth of pubic hair
Which lobe releases the hormone a?
a. Released by posterior lobe of pituitary, synthesized by hypothalamus
What inhibits LH?
c. Inhibin and moderate levels of estrogen inhibit LH
What is the name of the organ that gets converted by renin?
a. Liver (originally angiotensinogen but then gets converted by renin)
What is the name of the gland secreted by the zona fasciculate?
a. Secreted by zona fasciculate [adrenal gland]
Does high cortisol inhibit ACTH release?
c. High levels of cortisol inhibit release of ACTH, ACTH cannot make it to adrenal cortex to release glucocorticoids